Process for the activation of wood pulp prior to esterification



Feb. 18, 1947. J AY ETAL 2,415,949

PROCESS FOR THE ACTIVATION OF WOOD PULP PRIOR TO ESTERIFICATION Filed Dec. 5, 1944 7% 17m 17am fabwMQL ATTORN EYS Patented eh. 18, 1947 raocuss non THE AcTivATIoN or woon PULP PRIOR 'ro ESTECATION Judson H. Holloway, Robert S. Tabke, and Arthur llarrett, Shelton,

Rayonier Incorporated poration of Delaware Wasln, assignors to Shelton, Wash, a cor- Application December 5, 1944, Serial No, 566,658

Claims. (01. 260-229) This invention relates to wood pulp, especially to high-alpha wood pulp for acetylation, and has such pulp while impregnated with glacial acetic acid.

Wood pulp is usually supplied the producers of cellulose acetate in the form of a relatively dense sheet which is either wound in compact rolls or compressed into bales. The sheeted wood-pulp does not readily disintegrate in the mixture of acetylating agents to form a slush as it does in water and consequently the sheet usually must be sub-divided mechanically before being introduced into the acetylating equipment. The inactivity of machine-dried high-alpha wood pulp toward acetylation appears to be due to two different factors, one of which is the high-temperabeen subjected to a drastic disintegration operation; We have found that machine-dried high alpha-pulp which has been carefully carded by ture drying on the paper machine, and the other the mechanical grinding or flumng operation employed to sub-divide the sheet prior to acetyletion. If a wet sheet of non-mercerized wood pulp of suflicientlyl high alpha-cellulose content is dried at a temperature below 35 C. and then carefully carded or'torn by hand, it will be found to be 4 completely active toward acetylati'on. If, however, a machine-dried sheet of the same pulp be hand-carded or torn, it will be partially inactive,

due presumably to the action of high-temperature drying on the fibers. Now, if a sheet of the pulp which has been dried at a temperature below 35 C. is sub-divided by means vof a rotating picker-roll, hammer-mill, impact-attrition mill or other type of disintegrating equipment, the product will be partially inactive, to a degree de-' pending upon the particular machine used. This latter inactivation may-be due to the heating effect brought about by friction during the disintegration operation.

It is conceivable that the heating effect of drying and disintegration might even cause some partial depolymerization or degradation of the cellulose, at least in certain localized regions. It is thus apparent that in the case of machinedried high-alpha pulp which has been mechanically disintegrated, these two inactivatingeifects are additive, and so present a formidable obstacle 1 to satisfactory acetylation.

It has been the practice heretofore in overcoming the inactivity of wood pulp toward acetylation to pretreat the previously disintegrated sheet with from 15% to 50% of its weight of glacial acetic acid for a period of several hours. Although this procedure is quite eflectivein activating cellulose, pretreatment periods as long as 16 hours may be necessary for pulps that have hand requires at least a three-hour pretreatment; From-an industrial standpoint, this pretreatment is undesirable for many reasons, chief of which I is the necessity of providing a large volume of acid-proof storage space for the prolonged operation.

We have discovered that the machine-dried acetic acid and then disintegrating orflufiing by suitable mechanical means. The separated pulp fibers may then be acetylated at once in accordance with the conventional procedures, by employing acetic anhydride and sulfuric acid, in the presence of an excess of glacial acetic acid which serves as a solvent for the cellulose triacetate.

The invention accordingly provides an improved method 'of activating machine-dried-highalpha wood pulp which is both rapid and direct and which may be used effectively on pulps dried to a bone-dry condition. The invention may be very efiiciently and advantageously applied. in the activation of pulps dried tofrom 94% to 97.5% bone-dry. One important aspect of the invention is that the pulp may be dried to, say, around 97% bone-dry, and while still hot,- and before the pulp has an opportunity to absorb' moisture, impregnated with the desired quantity of glacial acetic acid. We have found that at least 15% and preferably from 20% to by weight of the air-dry pulp of glacial acetic acid is required for complete activation.

In an especially efl'ective'adaptation of the method of the invention, the sheet of pulp, while still hot from the drying operation, is impregnated with the glacial acetic acid, mechanically. disintegrated or fluffed and then acetylated at once, thus eliminating absorption of moisture, the storage of pulp while impregnated with acetic acid, and. the storage of disintegrated fibers. Moreover, the higher temperature of the glacial acetic acid, due to contacting the hot pulp, helps to overcome the inactivity.' I

The disintegrating or flufing should be carried out immediately following the impregnation with glacial acetic acid and is most desirably done under conditions which avoid or minimize grinding or rupturing the fibers.

The disintegrating may be done on any suitable mechanical apparatus, such as a rotating picker-roll, or prefering illustrates diagrammatically an arrangement,

.from the pulp-producer, i. e.,

rotating picker-roll I.

' out the final of apparatus suitable for carrying out a method of the invention.

In carrying out a method of the invention with apparatus of the type illustrated in the drawing, a continuous sheet of pulp from the pulp roll i is 5 unwound by means of the friction rolls 2. It is to be understood that roll I is merely illustrative of a suitable source of sheet cellulose. The roll may be passed through the apparatus as it comes withoutflnal drying, or it may be unrolled, passed through a. drying oven and then through the apparatus while containingmuch of its sensible heat. As illustrated in the drawing, the sheet from the roll is drawn through seal rolls 3 into an air-tight. chamber 4 and over the upper surface of a roll 5 of acid-resistant metal which dips into a bath ofglacial acetic acid 8.v The impregnated sheet, after passing between the two sets of rolls 2, is disintegrated or ilufled by means of the rapidly -2 The small rectangular baled sheets commonly used may also be impregnated with the glacial acetic acid with or withdrying, preferably by spraying the sheets before they are fed into rolls 2. It is advantageous to pass the sheet wet with glacial acetic acid into the disintegrating equipment at a. temperature above 20 C. and preferably at a temperature in the range of 50 C. to 70 C. The fluffed pulp falls through the hopper 8 into a suitable conveyor system 9 which carries it to temporary storage bins or, preferably, directly to the acetylators (not shown) Although the best results are obtained by using a heated pulp sheet, for example, one coming directly from the drying operation, yet we have found that entirely satisfactory activation may be effected by impregnating and disintegrating the sheeted pulp at ordinary temperatures.

The amount of acetic acid taken up by the sheet will depend on several factors, among which are the speeds and relative diameters of the rolls Sand 2, the physical surface characteristics of roll 5, and the depth to which the latter is immersed in the glacial acetic acid. Roll 5 may or may not be driven, depending upon its method of mounting and moment of inertia. It need not be of metallic composition but may be constructed from laminated fibrous material impregnated with a resin insoluble in acetic acid, e. g., one of the phenolformaldehyde type.- The immersed roller is merely illustrative of one suitable arrangement of impregnating apparatus. The pulp may be impregnated, for example, by spraying one or both surfaces of the sheet. For some types of grinding or comminuting equipment,

higher percentages'of acetic acid in the sheet may be desirable, but for the apparatus described above, amounts in excess of 150% tend to favor the formation of clumps or .knots of fibers rather than the open, fluffy structure which is highly. desirable. In a serie of tests varying predetermined quantitles of glacial acetic acid were caused to impregnate (both by spraying and absorption from a roller) strips of machine-dried high-alpha pulp which were dried to about 94% bone-dry, the proper quantities being gauged by weighing the pulp before and after impregnation. These strip were immediately flufied by means of the rotat- 7 mg picker-roll, after which they were subjected to acetylation without any further pretreatment. In the case of the samples which were not completely reactive, the percentage of unreacted material was determined by allowing the triacetate gum to stand until the portion which did acetylate had attained acetone solubility, after which a weighed aliquot portion of the thoroughly agitated gum was diluted with acetone and poured through a sintered glass funnel. The unreacted fibers were then washed with acetone, dried and weighed. The results are shown in Table I.

Table '1 Per cent Per cent HOAc on HOAc on Unwed fibers, per fibers, per wt. A. D. cent wt. A. D.

P lp p p o 6.60 to None 10 0. 50 None 20 0.31 None 40 None None For comparative purposes, the following tests were carried out in order to show the quantitative eifects of high-temperature dryi and of dry mechanical disintegration upon the activity toward acetylation and to demonstrate that the glacial acetic acid must be in contact with the pulp during mechanical disintegration in order to be efiective.

Test L-A sample of sheeted, machine-dried high-alpha pulp was carded by hand, after which it was acetylated without an acetic acid pretreatment.

Test II.-A wet sheet of the same high-alpha pulp containing approximately 50% water was allowed to dry in the air at 25 C. to a. 94% bonedry content; It was then carefully carded by hand and acetylated without an acetic acid pretreatment. I 7

Pest III.Th1s is-a repetition of Test 11 with the exception that the carding operation was carried out by means of the rotating picker-roll.

Test lV.Another portion of the same sheeted machine-dried high-alpha pulp was carded by means of the rotating picker-roll. The resulting fluff was then sprayed with 150% of its weight of glacial acetic acid and immediatelyacetylated without further acetic acid pretreatment.

In each of these experiments, the quantities of v unreacted material were determined as described above. The results are given in Table II.

Table II Unreacted Test flbers,,per

cent

T 3. 89 n Nona TIT 0. 95 IV 1. 12

It is apparent from the results of the foregoing tests that flufilng, or mechanical carding, in the presence of moderate quantities of glacial acetic acid, not only overcomes the inactivity of the pulp brought about by contact with the hot drier rolls of the paper machine, but also avoids the substantial inactivation which is normally effected by the dry iiufling action per se,,and

which is in evidence even when said dry flufling operation is carried'out on pulp which has not been subjected to previous high-temperature drying. -It is also evident that the same advantageous results cannot be attained by flufflng'machine-dried pulpand subsequently spraying with much larger proportions of glacial acetic acid.

When'this latter technique is employed, an ex-,

tended time oi pretreatment has been found to be necessary.

Table Another series of tests was carried out in which conditions were similar to those of the first series except that after flufiing, the mixtures of pulp these tests,- given in Table III, show again the advantage of fiufllng in the presence of acetic acid, since the conventional pretreatment step,

carried out on previously flufled machine-dried,

pulp by using 20% of glacial acetic acid on the weight of pulp, requires at least a three-hour period in order to bring about complete activation.

Table 111 Percent Percent HOAc on Unreacted HOAC on Unreacted fibers, per fibers, per wt. D. cent wt. D. cent P D D D 0. 31 25 None r 0. 075 30 None None 35 None None Still another series of tests was carried out on samples which had been fiuffed .after wetting the pulp sheet with 5% and 10% glacial acid based on the weight of air-dry pulp, the duration of pretreatment ranging upward to 16 hours. The results of'these are shown in Table IV.

I Table IV Unreacted fibers, per cent Pretreatment time, hrs.

, 5. get cent 10 per cent OAc HOAc that 10% of glacial acid based on the weight of air-dry pulp is not a suflicient amount to effect.

complete activation, even treatment. The data of with a prolonged pre- Table III indicate that a minimum of 15% is necessary if a one-hourpretreatment is to be used, while the results outlined in Table I show that somewhat more than 20% by weight of glacial acetic acid must be employed if immediate desired.

A series of other tests was made in which strips of machine-dried high-alpha pulp were heated in an oven at 105 C. for of time, whereby the bone-dry content was raised to 97.5%. After having been allowed to cool to room temperature in a desiccator, the strips of pulp were impregnated with predetermined quantitles of glacial acetic acid at 23 C. and flufied by means of-a rotating picker-roll. Samples of the fiuffed pulps were then subjected to acetylation without further pretreatment. series of tests was also carried out on pulp which had been dried'in the oven the same at 105 C.

to a 100% bone-dry content and subsequently cooled to room temperature in the desiccator. The results of these two series of tests are outlined in Table V.

a predetermined period A similar Unreacted flbers, per cent Acetic acid on weight 6m. D. pulp, per cent 91.5% B. D. 100.0% B. D. p lp p p complete activation is QOQO a arisesea These data show that high-alpha pulp which has been dried at 105C. to a bone-dry content of 97.5% may be completely activated by-disintegrating the sheets after treating them with 50% of glacial acetic acid based upon the weight of air-dry pulp. In the case of high-alpha pulpwhich has been completely dried B. D.) at C., a few unreacted fibers remain after acetylation in each case, but it will be noted that activation is substantially complete if this 100% B. D. pulp is impregnated with an app o a equal weight of glacial acetic acid (100% based on the weight of air-dry pulp) before disinte-. grating.

In the foregoing tables HOAc refers to "glacial acetic acid, the symbol Ac being an abbreviation for the acetyl radical CHaCO.

Another series of tests was carried out which shows the efiect of activation of machine-dried high-alpha pulp while still'hot as follows:

Test .-Machine-dried high-alpha pulp was further dried at 105 C. to tent. While still hot, it was mechanically carded by means of a picker-roll, after which it was acetylated without a pretreatment.

Test B.As a control test, machine-dried high-alpha pulp without being heated further, was mechanically carded by means of the pickerroll; then acetylated without pretreatment.

.Test "C.-Machine-dried high-alpha pulp was further dried at 105 C. to a 97.5% bone-dry content. It was thenimmediately impregnated'with glacial acetic tained 67.5% by'weight of glacial acetic acid, after which, it was carded at once by means of the picker-roll. Acetylation without further treatment was then efiected.

Test D.-This test was carried out in an analogous manner to the previous test except that the heated pulp sheet was impregnated with 91% by weight of glacial acetic acid, the temperature of which was 85 C.

Test .This test was similar to test except that the heated pulp sheet was allowed to cool in a desiccator, after which it was impregnated with 91% by weight of glacial acetic acid at a temperature of 23 C. Y

The results of these tests are shown in Table VI.

Table VI I Unreacted fibers, per cent Test These data indicate that the increased inacvity which is induced by additional high-tema 97.5% bone-dry con acid, the temperature of which was 23'C. to suchan extent that the mixture conperature drying of machine-dried high-alpha pulp may be substantially overcome by treating the hot pulp with either cold or hot glacial acetic acid immediately prior to mechanical disintegration. Al-

, though the results are no better than those obtained by cooling the dried pulp in a desiccator and impregnating with cold glacial acetic acid, yet they show that such cooling is not essential, and thus that a process wherein the heated sheet was treated immediately with either not or cold glacial acetic acid is advantageous.

In contrast to the slow, cumbersome methods of overcoming or avoiding the inactivity of machinedried high-alpha wood pulp toward acetylation, the method ofthis invention is both rapid and direct. Another advantage of this invention is the fact that the flufied or carded pulp is slightly damp, thus being free from the fine dusty material which is always present in pulp which has been disintegrated while in a dry state. Furthermore, the moist disintegrated product, because of its smaller bulk, may be much more readily handled on conveyors and may be charged into the acetylators much more readily than dry-flufied pulp. It is easily compacted into cotton-like clumps by the application of very slight pressures and this further adds to its ease of handling and charging. Y

In the work described herein, we refer to pulp containing about 6% moisture as air-dry" (abbreviation A. D.). This value represents the average equilibrium moisture content attained by high-alpha wood pulp when allowed to remain in temperature of approximately 20-25 C. A bone-dry pulp, as the term is used herein, is one from which all moisture has presumably been removed by heating in an oven 'at 105 C. for three hours. Thus, such a pulp-would be considered to be 100% bone-dry (abbreviation B. D.) while the air-dry pulp defined above would be 94% B. D. The term high-alpha refers to pulp which contains at least 95% of alpha-cellulose.

The references made herein to machine-dried high-alpha pulp do not apply to pulp which has been subjected to a mercerizing treatment, 1. e., to treatments with caustic soda solutions from to 30% in concentration and below a temperature of 35 C.

'I'he'methodof-this invention may be used in 1 esteriflcation generally as, for example, in the production of cellulose acetate propionate and cellu lose acetate butyrate. These compounds may be produced as mixed esters by introducing propionic acid and/or propionic. anhydride, or butyric acid and/or butyric anhydride, as the case may be,

into'the esterification mixture which contains, in

addition, acetic acid, acetic anhydride and sulfuric acid. The method of the present invention may be applied to the preparation of these compounds by impregnating the sheeted pulp with either acetic acid, a mixture of acetic and propionic or butyric acids, or propionic or butyric acid alone.

We claim:

1. The method of activating machine-dried high-alpha pulp in a pretreatment prior to acetylation which comprises impregnating the pulp while in sheet form with glacial acetic acid, and then immediately and while the acetic acid still is in contact with the pulp disintegrating the sheet by physically separating the fibers thereof to form a fluffy mass. I

2. The method of activating machine-dried high-alpha pulp which comprises impregnating the pulp while in sheet form with glacialacetic with'the pulp disintegrating the acid in an amount suflicient merely to dampen the'fibers and while the sheet contains heat from the drying operation, and while the acetic acid still is in contact with the sheet disintegrating it by physically separating the fibers to produce a fluffy .m'ass.

3. In the method of activating machine-dried high-alpha pulp, the improvement which comprises impregnating the pulp while in sheet form with glacial acetic acid in an amount varying from 15% to 150% based on the weight of the pulp, and while the acetic acid still is in contact sheet by physically separating the fibers thereof to produce a fluffy mass. I

4. The method of activating high-alpha sheet pulp dried to a moisture content of from 94% to 100% bone-dry which comprises impregnating the sheet with glacial acetic acid in an amount sufllcient merely to dampen the fibers, and immediately thereafter and while the acetic acid still is in contact with the pulp disintegrating the sheet by physically separating the fibers thereof to produce a flufiymass.

5. The method of activating high-alpha sheet pulp dried to a moisture content of from 94% to bone-dry in a pretreatment prior to acety- -lation which coinprises impregnating the sheet with glacial acetic acid while the sheet contains heat, from the drying operation, and immediately thereafter and while the acetic acid still is in contact with the pulp disintegrating the sheet by physically separating the fibers to produce a fluffy mass.

6. In'an operation for the production of cellulose acetate, the improvement which comprises drying high-alpha pulp in sheet form to from 94% to 100% bone-dry, impregnating the sheet with glacial acetic acid in an amount exceeding 15% by weight based on the weight of the air-dry pulp but not more than is necessary to dampen the pulp, and then-while the acetic acid still is in contact with the sheet of pulp disintegrating the sheet by physically separating the fibers to produce a-flufiy mass.

7. In an operation for the production of cellulose acetate, the improvement which comprises drying high-alpha pulp in sheet form on a drying machine to from- 94% to 100% bone-dry, 1mpregnating the sheet with glacial acetic acid in an amount sufllcient merely to dampen the fibers thereof while the sheet contains heat from the drying operation, disintegrating the sheet while the acetic acid still is in contact with the fibers thereof by physically separating the fibers to produce a flufiy mass, and passing the disintegrated .pulp at once to an acetylating operation, whereby drying high-alpha pulp in sheet form to from 94% to 100% bone-dry, impregnating the sheet with glacial acetic acid in an amount varying from 20% to by weight based on the weight of the pulp and while the sheet contains heat from the dryingoperation, disintegrating the sheet while the acetic acid still is in contact with the fibers thereof by physically separating the fibers to produce a fluffy mass, and passing the disintegrated pulp at once to an acetylating operation, whereby the fibers are'completely or substantially completely dissolved. 75

9. In an operation for the production of cellulose esters, the improvement which comprises impregnating a sheet of high-alpha cellulose with acetic acid and an acid from the group consisting of propionic acid and butyric acid in an amount suflicient merely to dampen the fibers of the sheet,

and then while the acids still are in contact with the fibers 0f the sheet mechanically disintegrating the sheet to produce a flufly mass.

10. In an operation for the production of cellulose esters, the improvement which comprises impregnating a sheet of high-alpha cellulose with I an acid from the group consisting of propionic acid and butyric acid in an amount sufllcient merely to dampen the fibers, and then while the acid still is in contact with the fibers of the sheet 15 mechanically disintegrating the sheet to produce a flufly mass.

JUDSON H. HOLLOWAY, ROBERT S. TABKE. ARTHUR N. PARRE'I'I'.

REFERENCES CITED The following references are of record in the 0 file of this patent:

NITED STATES PATENTS Number Name Date 2,150,690 Malm Mar. 14, 1939 2,026,986

Malm Jan. 7, 1936 

